Fixes bug with error pointers

- Adds validation in the ZCREasyRecipe's initializer
- Updates the deployment target to iOS 6.0+ and OSX 10.8+
- Converts ZCREasyProperty attributes from string constants to an
  enum.
- Adds ZCREasyDoughTransformer
Bumps version to 0.4.0
Merge branch 'develop' for 0.4.0